unless you have a thicknesser and jointer, or hand planes and lots of patience, sheet material will work much better for a desk top, it will be covered in crap within days anyway so you wont notice it, a good piece of birch ply makes a nice furniture surface once its lightly sanded and varnished,masking tape up the surface of the sheet before scribing helps stop chipout when cutting, try to use a fine blade in your jigsaw , and you could round over the front edge with a router. dont forget to swear like a trooper when doing it,along with cutting your finger, its traditional when doing home improvements